Depth sensing technology can be used to determine a person's location in relation to nearby objects or to generate an image of a person's immediate environment in three dimensions (3D). An example of depth sensing technology is a time-of-flight (ToF) depth camera. A ToF camera has a light source to emit light onto nearby objects. Light reflected off surfaces of the objects can be captured by the ToF camera. The time it takes for the light to travel from the light source of the ToF camera and reflect back from an object is converted into a depth measurement (i.e., distance to the object), which can be processed to map physical surfaces in the user's environment and, if desired, to render a 3D image of the user's environment. Another example of ToF based depth sensing technology is based on phase delay calculations. Emitting light at one or more known frequencies and comparing the phase of received reflected light with that of the emitted light enables a calculated phase delay. Knowing one or more phase delays of the reflected light enables a processor to determine the distance to the object from which the light was reflected.
Depth cameras and their associated illumination systems require power to operate. In mobile devices, there are often strict constraints on power consumption, as well as size, weight and cost. Where more frequent emissions from an illumination module are used, the power consumption increases. This issue is present in a number of devices such as depth sensing devices, active infrared (IR) modules, night vision cameras, security cameras, and other applications of machine vision. The frequency and duration of the illumination of these systems is typically chosen to meet desired levels of accuracy at a given moment, or to increase operational range of the active imaging system. Higher frame rates provide higher certainty for the current location of objects within view of the depth sensor. Higher accuracy and precision of the depth sensor improves the performance of applications that consumes an output depth map. A device designed to provide active illumination at a high frame rate tends to require a power source (e.g., one or more batteries) with more capacity, and therefore more size and weight, than a device that uses a lower frame rate, thereby undesirably adding to the size, weight and cost of the end product.